The present invention relates to a printer apparatus, a printer system, and a driving method of a printer apparatus in which ink and a diluent (liquid) are mixed with each other immediately before being jetted onto a recording medium.
The document publishing using a computer which is called desk top publishing has become popular particularly in offices and like environments. In recent years, there have increased demands for, outputting a color photo-like image such as a photograph together with a text and/or a figure a rather than outputting only a text and/or a figure. Therefore, now it is required to print a high-quality photo-like image and the expression of gradation using halftone display is important.
In recent years, what is called an on-demand printer apparatus which performs recording by jetting ink droplets from nozzles only when necessary during printing in accordance with control signals that correspond to recording signals, to thereby deposit the ink droplets on a recording medium such as a sheet or a film has spread at high speed because it is suitable for miniaturization and cost reduction.
Although various methods for jetting an ink droplet from a nozzle as mentioned above have been proposed, a method using a piezoelectric element and a method using a heating element are now commonly used. In the former method, ink is jetted by applying pressure to it by utilizing deformation of a piezoelectric element. In the latter method, ink is jetted by pressure of bubbles that are generated by heating and vaporizing ink in a nozzle with a heating element.
There have been proposed various methods for simulating, in the above-mentioned on-demand printer apparatus that jets ink droplets, the above-mentioned expression of gradation using halftone display. In a first method, the gradation is expressed by controlling the size of a jetted droplet by varying the amplitude or pulse width of a voltage applied to a piezoelectric element or a heating element and thereby making the printing dot diameter variable.
However, in the first method, if a voltage applied to a piezoelectric element or a heating element is too low or its pulse width is too small, ink is not jetted. Therefore, the minimum droplet diameter has a certain limit, which causes a problem that the number of expressible gradation levels is small and particularly a problem that it is very difficult to express low-density levels. The first method is thus insufficient for printing of a photo-like image.
In a second method, each pixel is formed by a matrix of, for instance, 4xc3x974 dots without varying the dot diameter and the gradation is expressed by performing image processing of what is called a dither method or an error diffusion method on a matrix-by-matrix basis.
However, in the second method, although densities of 17 gradation levels can be expressed when each pixel is formed by a 4xc3x974 matrix, the resolution is lowered to xc2xc if, for instance, printing is performed with the same dot density as in the first method, in which case a resulting image may have marked roughness. Therefore, the second method is also insufficient for printing of a natural image.
In view of the above, to solve the problems of the conventional on-demand printer apparatuses in terms of the principle of operation, the present inventors proposed a printer apparatus having an external mixing type printer head which performs recording by forming an ink liquid by mixing ink and a transparent solvent as a dilute at a given mixing ratio and jetting the ink liquid immediately thereafter to deposit it on a recording medium (for example, refer to Japanese Unexamined Patent Publication Nos. Hei. 5-201024 and Hei. 7-195682).
In the printer head of this printer apparatus, a quantifying nozzle is provided adjacent to a jetting nozzle and a quantified ink liquid is deposited on a recording medium in the following manner.
First, ink of a predetermined amount flows out of the quantifying nozzle and moves to the jetting nozzle and its vicinity. Then, a dilute is jetted from the jetting nozzle and mixed with the ink existing at the jetting nozzle and its vicinity at this time, to form an ink liquid having a desired-ink density. A droplet of the thus-mixed ink liquid is jetted toward a recording medium and deposited thereon.
In the above carrier jet printer apparatus, the density of a mixed solution that is jetted is controlled by varying the mixing ratio between ink and a dilute by changing the amount of a quantifying medium that is the ink or the dilute. In this manner, the density can be varied on a printed dot basis. Therefore, it is possible to print out a photo-like image with many intermediate gradation levels without lowering the resolution.
In the above carrier jet printer apparatus, the relationship between a drive signal that is applied to a quantifying-medium-side or jetting-medium-side pressure generating section, particularly the quantifying-medium-side pressure generating section, and the density of an ink liquid formed by quantifying and then mixing a quantifying medium and a jetting medium is not a simple relationship such as a proportional relationship.
That is, in the printer head of the carrier jet printer apparatus, there may occur an event that when a drive voltage is applied to the quantifying-medium-side pressure generating section based on a drive signal obtained by converting a print signal, if the drive voltage is low particularly a quantified ink is pushed out from the quantifying nozzle only to inflate and does not reach the vicinity of the jetting nozzle. As a result, when a dilute is jetted from the jetting nozzle, it cannot be mixed with the ink. In this case, only the dilute is deposited on a recording medium.
Therefore, the above mentioned printer apparatus has a problem that gradation levels cannot be expressed in a desired manner when the printer head is driven by using drive signals obtained by converting print signals.
The present invention has been made in view of the above circumstances in the art, and an object of the invention is therefore to provide a printer apparatus, a printer system, and a driving method of a printer apparatus which can control, with high accuracy, the density of an ink liquid that is a mixture of ink and a dilute so that it becomes a desired value, and which can therefore express gradation levels in a desired manner.
A printer apparatus according to the invention that has been completed to attain the above object comprises a converting section for converting an input signal that includes information on dots to be printed into a print signal that is necessary for printing by performing predetermined conversion processing on the input signal; and dot printing means for printing dots on a recording medium by forming an ink liquid for each dot by mixing ink and a dilute in a predetermined ratio based on the print signal, and jetting the ink liquid onto the recording medium.
In particular, in the printer apparatus according to the invention, the converting section converts the input signal into the print signal so that the dot printing means mixes the ink into the dilute even in a case where printing is performed based on an input signal that includes a dot information which is below a threshold density determined by the dot printing means.
In the above-configured printer apparatus according to the invention, since the converting section is provided that converts the input signal into the print signal so that the dot printing means mixes the ink into the dilute even in a case where printing is performed based on an input signal that includes information on a dot of the lowest density, ink of a correct amount can be mixed into a dilute even when printing is performed based on an input signal of a low density. Therefore, correct gradation expression is enabled, and there can be avoided a phenomenon that quantified ink is not mixed with a dilute even if the dot printing means is driven.
The converting section need not always be provided in the printer apparatus, and may be provided outside the printer apparatus and connected to it as in the case of a printer system according to the invention.
That is, the printer system according to the invention comprises a converting section for converting an input signal that includes information on dots to be printed into a print signal that is necessary for printing by performing predetermined conversion processing on the input signal; and a printer apparatus comprising dot printing means for printing dots on a recording medium by forming an ink liquid for each dot by mixing ink and a dilute in a predetermined ratio based on the print signal, and jetting the ink liquid onto the recording medium.
In particular, in the printer system according to the invention, the converting section converts the input signal into the print signal so that the dot printing means mixes the ink into the dilute even in a case where printing is performed based on an input signal that includes a dot information which is a threshold density determined by the dot printing means.
In the above-configured printer system according to the invention, since the converting section that performs the above conversion processing is provided, ink of a correct amount can be mixed into a dilute even when printing is performed based on an input signal of a low density. Therefore, correct gradation expression is enabled, and there can be avoided a phenomenon that quantified ink is not mixed with a dilute even if the dot printing means is driven.
A driving method of a printer apparatus according to the invention comprises the steps of converting an input signal that includes information on dots to be printed into a print signal that is necessary for printing by performing predetermined conversion processing on the input signal; and printing dots on a recording medium by forming an ink liquid for each dot by mixing ink and a dilute in a predetermined ratio based on the print signal, and jetting the ink liquid onto the recording medium.
In particular, in the driving method of a printer apparatus according to the invention, in the predetermined conversion processing the input signal is converted into the print signal so that the ink is mixed into the dilute even in a case where printing is performed based on an input signal that includes information on a dot of the lowest density.
In the above-configured driving method of a printer apparatus according to the invention, since the above conversion processing is provided, there can be avoided a phenomenon that quantified ink is not mixed with a dilute even if a dot printing means is driven.